The invention relates generally to ventilators for supporting ventilation in air breathing mammals, both humans and animals. More particularly, the present invention relates to high frequency ventilators which operate by supplying oscillating respiratory gases to a patient at a frequency above the normal breathing frequency of the patient.
High frequency oscillating ventilators are well known and have been previously described in, e.g., U.S. Pat. No. 4,719,910, which is incorporated hereby by reference in its entirety. Unlike conventional ventilators which ventilate by positive-pressured gas flow and rely on passive recoil of the lung tissue for expiration, high frequency oscillating ventilators employ an active expiratory phase in which gas is pushed into and pulled out of a patient's lungs during alternate half-cycles of the oscillating diaphragm (or piston) of the ventilator. The forward motion of the diaphragm (toward the patient) creates a positive-going pressure relative to the static pressure in the patient's airway. As the diaphragm is driven rearward from its most forward position, the dynamic pressure it generates reverses from positive-going to negative-going. This bipolar dynamic pressure waveform is the principle reason for the success of the high frequency oscillating ventilator in providing improved respiratory gas exchange.
A problem that has been encountered in the use of high frequency oscillating ventilators of the type disclosed in the aforesaid U.S. Pat. No. 4,719,910 is that gases, vapors, and secretions, in other words, fluids, from the lungs and airways of a patient return with the expired air, and may contaminate all parts of the oscillating ventilating machine which they directly contact or to which they may migrate. While patient endotracheal tubes and associated parts and connections used for the introduction of gas, anesthetics, medications, etc. to a patient are generally disposed of when transferring the high frequency oscillating ventilator from one patient to another, the vibrator unit, which produces the oscillating pulses of air or oxygen, cannot be disposed of because of the relatively high cost of manufacture of such units. Therefore, in order to avoid cross-contamination or cross-infection between patients, time consuming and rigorous cleaning and disinfection procedures have been a necessary and expensive step preceding the transfer of the high frequency oscillating ventilation machine from one patient to another.